Since the beginning of the 20th century, when F. W. Taylor used water for the first time to cool the machining process and concluded it increased tool life, a large variety of cutting fluids has been used with this and other purposes. However, in the last decade a lot has been done aiming to restrict the use of cutting fluids in the production, due to the costs related to the fluids, ecological issues, and human health and so on. (Helsel et al., 1998)
There are several ways of classifying cutting fluids and there is no standardization to establish one of them within the industries. The most popular classification gathers the products like the following classification—
I. Air
II. Water Based Cutting Fluids:
                a) Water;        b) Emulsions (soluble oil);        c) Chemical solutions (or synthetic fluids);III. Neat Oils:        a) Mineral oils;        b) Fatty oils;        c) Composed oils;        d) Extreme pressure oils (EP);        e) Multiple use oils.        
Metal-cutting fluid, an indispensable additive in metal-cutting process, has functions of lubricating, cooling, cleaning, and anti-rust and etc. It has remarkable effects on increasing the durability of cutter and the efficiency of production, improving the product quality, and prolonging the service life of cutter, in turn prolongs the service life of machine and ensures the stability and reliability of working conditions of machine. Therefore, research on cutting fluid technology, as well as improvement of cutting fluid quality play important roles in the modern mechanical processing industry. However, many commercially available cutting fluids contain organic sulphur, chlorine, nitrite and etc. that are harmful to the human body and environment, which have severely negative effects on their applications (Feng, Jufen et al, 1995, p. 40-43).
Traditionally, cutting fluids have been widely used in machining operations in efforts to increase cooling and lubricity, and as a result enhance tool life, reduce process variability, etc. However, over the last decade, it has become apparent that fluid-related decisions have all too frequently been based upon industrial folklore rather than knowledge-based quantitative evidence. Recently there has been a change in this situation, in part driven by the fact that costs associated with fluid use often constitute between 7% and 17% of total production costs, as compared to 4% for tooling costs (King et al., 2001).
Over the past decade, cutting fluids have been studied extensively to characterise their relative benefits and shortcomings in terms of their use within machining processes. Traditionally, manufacturers have employed cutting fluids to serve the following functions: cooling, lubrication, corrosion inhibition, and chip flushing, and as a result, achieve such benefits as increased tool life, improved workpiece quality, enhanced machine tool life, and effective chip management. (Skerlos et al., 2000; Skerlos et al., 2001)
Soluble oils as the emulsions are popularly known are bi-phase composites of mineral oils added to water in proportion that varies from 1:10 to 1:100. It contains additives (emulsifiers) to allow the mixture of oil particles and water. These additives decrease the surface tension forming a stable monomolecular layer in the oil-water interface. Therefore these additives provide the formation of small particles of oil, which can result in transparent emulsions. (J. Braz. Soc. Mech. Sci. vol. 23 no. 2 Rio de Janeiro 2001)
Soluble oils are special types of mineral oils emulsified in water at concentrations between 5 and 20%, with lower concentrations (less than 10%) being most common in general purpose machining. Soluble oil concentrates contains severely refined base oils (30 to 85%), emulsifier and performance additives such as extreme pressure additives, stabilizers, rust inhibitors, defoamers and bactericides. The oil viscosity is typically 100 Saybolt Universal Seconds (SUS) at 100° F. (100/100 oils); higher viscosity oils provide better lubricity but are more difficult to emulsify.
Emulsifiers are added to form stable dispersion of oil in water; emulsifier particles are located around the oil droplets to give them a negative charge that will bound them with the water molecules. The size of the emulsified oil drops is very critical to fluid performance; it is easier for the smaller emulsion sizes to penetrate the interface of the cutting zone. (David A. Stephenson. John S. Agariou. “Metal cutting Theory and Practice, 2nd edition, pg—769)
Reference can be made to U.S. Pat. No. 4,778,614 wherein a composition for the preparation of a soluble-oil for use in a cutting fluid comprises a mineral oil and, as an emulsifier, an effective amount of a sulphonate of a branched polymer of C3 to C5 olefin. Preferably the polyolefin chain of the sulphonate has an average molecular weight in the range 275 to 560 and the polyolefin is polyisobutene is been disclosed.
Reference can be made to British Patent 2252103 which discloses that such oil-containing fluids may create a mist at the site of the work piece being operated on or when the fluid is sprayed and such mist travels through the air in the vicinity of the machine and the operator thereof.
Reference can be made to U.S. Pat. No. 6,204,225 wherein it is disclosed that the additives in conventional metal working fluids used for metal removal often contain large amounts of sulfur. These can be in the form of sulfurized oils, sulfonates, or sulfates. The presence of significant amounts of sulfur in a metal working fluid provides nutritional sustenance for anaerobic sulfate-reducing bacteria, resulting in formation of hydrogen sulfide in the operating system. Hydrogen sulfide is extremely corrosive in very small quantities and produces an objectionable odor. Higher concentrations of hydrogen sulfide can also cause health problems.
Reference can be made to EP20080015630 which discloses about the use of an alkoxylated fatty alcohol containing at least water and one oily component, non-miscible with water, and optionally further ingredients common for metal working fluids.
Reference can be made to U.S. Pat. No. 7,968,504 which provides a composition that includes a transesterified fatty acid ester resulting from the reaction of a fatty acid ester, in the presence of an acid, with a hydroxyl-containing compound. The resulting composition is useful as a lubricant, as a heat transfer agent, as a rheological modifier and as a corrosion/moisture inhibitor, among other uses.
Reference can be made to US20120184475 which disclose a water-soluble metalworking oil agent provided by blending the following components A, B, C and D. The water-soluble metalworking oil agent is excellent in friction modification between a tool and a material, so that the water-soluble metalworking oil agent can significantly prolong the lifetime of the tool even when being applied to so-called difficult-to-machine materials such as titanium and a titanium alloy.